Abstract: A data terminal utilizes a time division multiplexer to monitor traffic on up to 8000 input lines in banks of 1000 lines and converts the information in each bank from parallel to serial form as 1000 serial 112 bit parallel words, records the various kinds of event count data and usage time duration for each input line, and under interrogation by a control center transmits the accumulated data.The terminal has up to eight serial synchronously operating memory banks, one for each bank of 1000 lines, each memory bank containing an accumulating memory which counts the events as they occur and a passive memory which upon command receives data from the accumulating memory. The condition of each line is examined continuously cyclically to determine the presence or absence of specifically different particular events and the durations of such events. The accumulated data is usable directly for billing purposes when the apparatus is used to monitor telephone subscriber lines.